1. Field of the Invention
The present invention relates to a method of forming a pattern on the surface of a semiconductor wafer.
2. Description of the Related Art
The process of manufacturing a semiconductor device involves a number of patterning steps wherein a plurality of materials are deposited respectively as a working film (film to be worked) on a silicon wafer, the resultant deposited layers being formed into desired patterns. The patterning of the working film can be performed as follows. First of all, a photosensitive material generally called a resist is deposited on the surface of working film to form a resist film, and then, a prescribed region of the resist film is subjected to an exposure process. Thereafter, the exposed or unexposed portion of the resist film is removed by means of a development process to thereby form a resist pattern. Finally, the working film is dry-etched using the resist pattern as an etching mask.
As for the exposure light source to be employed in the exposure process, an ultraviolet ray such as a KrF excimer laser, ArF excimer laser, etc. has been employed in view of throughput. However, due to the recent trend to further miniaturize an LSI, the resolution is now required to be controlled to as fine as not more than the wavelength of the ultraviolet ray. As a result, the tolerance in the exposure process such as the exposure tolerance dose or the focusing tolerance is now becoming insufficient for meeting such a trend. It may be effective, for the purpose of making up for these process margins, to make the resist film thinner in thickness to thereby improve the resolution of the resist film. This however leads to the problem that it becomes difficult to secure a sufficient film thickness of resist layer which is required for etching the working film.
With a view to overcome this problem, a pattern transfer method is now employed, wherein a resist pattern is transferred to a silicon oxide film to form a silicon oxide film pattern, which is then employed as an etching mask in the dry-etching of a working film.
As for the silicon oxide film to be employed in this case, a spin-on glass has been employed because of the simplicity of the coating method for forming a film thereof. However, the employment of this spin-on glass is accompanied with the problem that the spin-on glass may be ruptured on the occasion of etching a working film, thereby making it difficult to properly work the working film.